The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load.
In a healthy intervertebral disc, cells within the nucleus pulposus produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus with its cushioning qualities. These nucleus pulposus cells may also secrete small amounts of cytokines as well as matrix metalloproteinases (MMPs). The cytokines help regulate the metabolism of the nucleus pulposus cells.
In some instances of disc degeneration disease (DDD), gradual degeneration of the intervertebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased or unconventional loads and pressures on the nucleus pulposus cause the cells to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors or apoptosis can also cause the cells within the nucleus pulposus to emit toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to eliminate waste may result in the accumulation of high levels of toxins which leads to nerve irritation and pain.
As DDD progresses, the toxic levels of the cytokines present in the nucleus pulposus begin to degrade the extracellular matrix. In particular, the MPPs (as mediated by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing its water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the loading pattern within the disc, thereby possibly causing delamination of the annulus fibrosus. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, and thereby typically upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain.
Conventional technology for treating such pain includes the replacing the degenerating disc with either a fusion cage or a motion disc. The literature related to such treatments details the use of both spreader blocks and intra-discal balloons within the intradiscal space. Various spreader blocks are frequently utilized to loosen disc tissue, expand/regain disc height, and encourage vertebral body endplate vascularity. General in-situ balloon art also includes stand alone implants and balloons reinforced with bands, fabrics or scaffolds to enable directional growth.
U.S. Pat. No. 6,632,235 (Weikel) discloses a balloon for insertion into the disk space and inflated to distract the vertebrae. The controlled inflation of the balloon may ensure optimum distraction of the vertebrae and facilitate maximum implant height and neural foraminal decompression. If the balloon is to serve as a distraction instrument, a bone or synthetic allograft along with cancellous bone graft or filler material may then be implanted into contralateral disc space. Once the implant and other materials are in the desired position, the balloon may be deflated and removed from the disk space and a second implant of the same height may be inserted into that space. If the balloon is to serve as a spacer for intervertebral body fusion, the balloon may be inflated with a filler material that sets to form an synthetic allograft implant in vivo. Once the implant has been adequately formed, the balloon may be lysed and removed from the disk space. In another example, the inflated balloon is left intact and is separated from the catheter to remain within the disk space as a scaffold for new bone growth. As previously described, a balloon implant also may be resorbed by physiological conditions and expelled from the patient or transformed and remodeled into new bone growth.
U.S. Pat. No. 6,332,894 (Stalcup) discloses an orthopaedic implant for implanting between adjacent vertebrae and a spine, includes a generally annular bag; and a hardened polymer with the bag. The method of fusing adjacent vertebrae in a spine includes the steps of forming an access hole in an annulus of a disc between the adjacent vertebrae; removing the nucleus within the disc to form a cavity surrounded by the annulus; placing a generally annular bag within the cavity; filling the bag with a polymer; injecting bone particles into the cavity surrounded by the annular bag; and hardening the polymer.
US Published Patent Application 2006/0264945 (Edidin) discloses a scaffold configured to be disposed in a bone. The scaffold is configured to move from a first configuration to a second configuration. The scaffold in the second configuration is expanded from the first configuration. A selectively-expandable actuator is configured to be removably disposed within the scaffold. The selectively-expandable actuator is configured to move at least a portion of the scaffold to the second configuration when the selectively-expandable actuator is moved to an expanded configuration. A shape of the selectively-expandable actuator is substantially the same as a shape of the scaffold when the selectively-expandable actuator and the scaffold are in the second configuration. The selectively-expandable actuator configured to be removed from the scaffold when in a collapsed configuration. The scaffold is configured to remain substantially in the second configuration after the scaffold has been expanded by the actuator.
US Published Patent Application US2005/0070900 (Serhan) discloses an intervertebral fusion device includes a body having a proximal portion along a major axis of the body and a distal portion along the major axis, and supporting means at the distal portion. The supporting means supports vertebrae in a distracted position while the vertebrae fuse. At least one of the body and the supporting means has a height distinct from a width, whereby the body or supporting means can distract vertebrae, between which the body or the supporting means has been placed, by rotation of the body or the supporting means about the major axis. A method of fusing vertebrae includes the steps of inserting between two vertebrae an intervertebral fusion device and rotating the body or the supporting means, whereby the vertebrae are supported in a distracted position while the vertebrae fuse. US2004/0073213 (Serhan) discloses a device for distracting two vertebral bodies and delivering a flowable material into the disc space, comprising a body having a proximal portion and a distal portion, the distal portion having a shape adapted to distract, the body also having a longitudinal bore defining a first outlet port in the distal portion, and a first injection port in the proximal portion.
US Published patent applications US2005/0070900 and US2004/0073213 disclose fluid dispensing through a spreader block. These applications require the balloon(s) to be in direct fluid communication with the spreader.